A long time ago by which I mean prior to a certain infamous date in September I used to stand at the salad bar and wonder if I was taking my life in my hands.

All that food, out in the open and unmonitored. What a simple matter for a sick mind to poison it. How many people would die before anybody figured it out? It struck me that mass murder by proxy would be distressingly easy to pull off because a society is vulnerable at so many points. Sprinkle something on the food, spray something in the air, slip something into the mail.

Disturbing thoughts, yes. Which is why I preferred not to think about them. After all, nothing bad was going to happen, so why worry about how exposed we were? We lived at the end of history, beyond the reach of cataclysm. Somehow, you just knew this.

It is, of course, different now.

Which is why something the secretary of defense wrote the other day resonated with me. In a Nov. 1 essay on the op-ed page of The Washington Post, Donald Rumsfeld argued that it’s time for the nation to prepare for its next war. Meaning, not the war currently being waged in Afghanistan, but the one that will follow that.

To do this, he wrote, the military itself must change. Historically, the Defense Department has based its planning on determining from which nation the next threat was likely to come. In his ideal model, the department would focus less on who than how, working to figure the ways in which an adversary any adversary might attack. The military, said Rumsfeld, ought to be able to anticipate an enemy’s use of “surprise, deception” and “asymmetric weapons” meaning anthrax and hijacked airplanes and defend accordingly.

In other words, we may pride ourselves on having the world’s mightiest military, but that’s of limited significance if that military isn’t prepared to confront the threat at hand. You might own the world’s best hammer, but if the job requires a socket wrench, you might as well not have any tools at all.

The secretary, by the way, was pushing military reorganization before the recent tragedy. The difference is that we’re listening now.

Small wonder. Seeing skyscrapers fall has traumatized us. Now we endure the water torture tension of anthrax revelations every day. The notion that we live beyond history a notion born of 25 years of stability, rising living standards and relative peace has been emphatically shattered. We’ve lost the delusion of our own invulnerability. Worse, we have discovered ourselves to be woefully unprepared to cope with the world as it is.

After Sept. 11, we learned that our intelligence capabilities have been eroding for years. The FBI was reduced to issuing a public plea for help from anyone who speaks Arabic. And last week, in an era of allegedly heightened airport security, a Mississippi man managed innocently and inadvertently, thank goodness to bring a gun through airport security and onto a flight.

Vulnerable at so many points. And the thing that’s difficult for intellect to process is that we always will be. You can’t station soldiers at the salad bar. You can’t guard against everything.

But you can try.

One of the burdens of living in unfolding history is that you’re forced to take the world as it is, not as you wish it to be.

What the secretary preaches for the military ought to be gospel to the rest of society, a mandate to every manager, mayor and magistrate. We have to do more than react. Have to not only close our vulnerability to the present threat, but learn to anticipate and foreclose the next one as well. And yes, remain an open and tolerant society.

If that sounds like a tall order, it is. But then, the changes demanded of us by recent events are nothing less than seismic. One of the burdens of living in unfolding history as opposed to at its end is that you’re forced to take the world as it is, not as you wish it to be.

So we must figure out where we are vulnerable. And the need is urgent.

Because somebody out there already knows.

Leonard Pitts is a columnist with the Miami Herald.